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United States Patent |
5,659,202
|
Ashida
|
August 19, 1997
|
Semiconductor device with a pair of dummy electrodes below an inner lead
Abstract
A semiconductor device is provided which comprises: a semiconductor chip
having a semiconductor substrate, an insulation a film, a field oxide film
and pads formed on a surface thereof; bumps respectively formed on the
pads; inner leads bonded to the semiconductor chip with intervention of
bumps; a metal interconnection formed in an indentation which is formed
between the pads and an edge of the semiconductor chip by removing part of
the insulation film and/or the field oxide film of the semiconductor chip;
and a pair of dummy electrodes respectively formed between each of the
pads and the metal interconnection and between the metal interconnection
and the edge of the chip at a higher elevation than the metal
interconnection and spaced apart a predetermined distance from the metal
interconnection, the pair of dummy electrodes being provided for each of
the inner leads, which is located thereabove.
Inventors:
|
Ashida; Tsutomu (Nara, JP)
|
Assignee:
|
Sharp Kabushiki Kaisha (Osaka, JP)
|
Appl. No.:
|
630624 |
Filed:
|
April 10, 1996 |
Foreign Application Priority Data
Current U.S. Class: |
257/758; 257/E23.021; 257/E23.151 |
Intern'l Class: |
H01L 023/29; H01L 027/118 |
Field of Search: |
257/758,211,207,208,210
|
References Cited
U.S. Patent Documents
5381030 | Jan., 1995 | Kasai | 257/211.
|
Foreign Patent Documents |
60-79744 | May., 1985 | JP | 257/758.
|
1-152644 | Jun., 1989 | JP | 257/758.
|
1-303742 | Dec., 1989 | JP | 257/758.
|
2-260425 | ., 1990 | JP | 257/758.
|
3-169073 | Jul., 1991 | JP | 257/758.
|
3-190236 | Aug., 1991 | JP.
| |
3-263325 | Nov., 1991 | JP.
| |
3-274764 | Dec., 1991 | JP | 257/758.
|
5-343540 | Dec., 1993 | JP | 257/211.
|
6-77223 | Mar., 1994 | JP.
| |
6-97300 | Apr., 1994 | JP | 257/758.
|
Primary Examiner: Crane; Sara W.
Assistant Examiner: Williams; Alexander Oscar
Attorney, Agent or Firm: Nixon & Vanderhye P.C.
Claims
What is claimed:
1. A semiconductor device comprising:
a semiconductor chip having a semiconductor substrate, an insulation film,
a field oxide and pads formed on the field oxide;
bumps formed on the pads;
inner leads for making external connections to the chip bonded to the pads
at the bumps and extending in spaced apart relationship above and beyond
an edge of the chip;
a metal interconnection formed in an indentation which is formed between
the pads and the edge of the chip, the indentation being formed in at
least one of the insulation film and the field oxide;
a pair of dummy electrodes respectively formed between each of the pads and
the metal interconnection and between the metal interconnection and the
edge of the chip at a higher elevation than the metal interconnection and
spaced apart a predetermined distance from the metal interconnection, the
pair of dummy electrodes being provided for each of the inner leads, which
is located there above, and separate from other pairs of dummy electrodes
provided for other inner leads.
2. A semiconductor chip as set forth in claim 1, wherein the metal
interconnection is formed directly on the semiconductor substrate in the
indentation.
3. A semiconductor device as set forth in claim 1, wherein the dummy
electrode is formed as a single-layer structure.
4. A semiconductor chip as set forth in claim 1, wherein the dummy
electrode is a film formed simultaneously with the formation of the metal
interconnection about 200 nm to 1000 nm in thickness and about 0.2 .mu.m
to 10 .mu.m in width.
5. A semiconductor chip as set forth in claim 1, wherein the dummy
electrode is a film formed simultaneously with the formation of the metal
interconnection.
6. A semiconductor device as set forth in claim 2, wherein a diffusion
layer is formed in the semiconductor substrate where the metal
interconnection is formed directly on the semiconductor substrate.
7. A semiconductor device as set forth in claim 6, wherein the diffusion
layer and the semiconductor substrate are of the same conductivity type.
8. A semiconductor device as set forth in claim 6, wherein the diffusion
layer and the semiconductor substrate are of opposite conductivity type.
9. A semiconductor device as in claim 1 wherein the dummy electrodes are
formed as a double-layer structure.
10. A semiconductor device as in claim 1 wherein an insulating film is
formed over the pair of dummy electrodes.
11. A semiconductor device comprising;
a semiconductor substrate,
a field oxide film formed on one surface of the substrate,
a contact pad formed on the field oxide film,
an insulating film with a through-hole at the contact pad formed on the
field oxide film,
a bump formed on the contact pad in the through-hole and extending above
the insulating film,
an inner lead bonded at one end to the contact pad at the bump and
suspended over the insulating film and an edge of the substrate,
a metal interconnection formed between the contact pad and the edge of the
substrate and crossing under the inner lead, and
means for preventing the inner lead from sagging into contact with said
metal interconnection and the edge of the substrate, said means comprising
a pair of dummy electrodes with one of the dummy electrodes disposed below
the inner lead, between and spaced from the contact pad and the metal
interconnection, and with the other of the dummy electrodes disposed below
the inner lead, between and spaced from the metal interconnection and the
edge of the substrate.
12. A semiconductor device as in claim 11 wherein each dummy electrode is
formed as a double-layer structure.
13. A semiconductor device as in claim 11 wherein each dummy electrode is
of a predetermined limited area.
14. A semiconductor device as in claim 13 wherein each dummy electrode
extends above the height of the metal interconnection.
15. A semiconductor device as in claim 11 including a plurality of contact
pads and a plurality of inner leads bonded to the contact pads by bumps,
the plurality of inner leads being suspended over the insulating film and
extending over the edge of the substrate with the metal interconnection
formed between the pads and the edge of the substrate, and a plurality of
said means for preventing the inner leads from sagging into contact with
said metal interconnection and the edge of the substrate, one such means
for each inner lead, wherein the one dummy electrode of each pair and the
other dummy electrode of each pair, each comprises a discrete electrode
disposed in a line of discrete dummy electrodes parallel to the metal
interconnection.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a semiconductor device and, more
particularly, to a semiconductor device fabricated with a chip design for
preventing an inner lead from contacting an edge and a metal
interconnection of a semiconductor chip of a tape carrier package (TCP)
which is one type of semiconductor packages.
2. Description of Related Arts
A tape carrier package is one type of conventional semiconductor device. In
the semiconductor device of this type, as shown in FIG. 5, an external
interconnection (inner lead) 11 is bonded to a bump 9 which is formed on a
surface of a semiconductor chip 1a having various devices and circuits
with intervention of a pad (not shown).
To fabricate the semiconductor package with the aforesaid construction, the
semiconductor chip 1a having the bump 9 is set on a bonding stage 16. In
turn, the bump 9 is positioned in alignment with the inner lead 11
extending from a device hole for mounting a chip of a tape carrier 15.
Thereafter, the inner lead 11 and the bump 9 are heated and pressed by
means of a bonding tool 14 for eutectic bonding therebetween. The bump 9
and the inner lead 11 are generally plated with gold and tin,
respectively, and therefore the bonding between the bump 9 and the inner
lead 11 is achieved by forming a eutectic alloy of gold and tin
therebetween.
The pad of the semiconductor chip is generally formed in a peripheral
region of the chip. In some cases, a metal interconnection such as a power
supply line is provided between the pad and an edge of the chip because of
restriction on circuit arrangement. As shown in FIGS. 6 and 7, an
insulation film 5 is formed in a device formation region on an active
region and a field oxide film 2 which is formed on a region other than the
active region of a semiconductor substrate 1, and the metal
interconnection 17 is formed on this insulation film 5. The inner lead 11
crosses the metal interconnection 17 as shown in FIG. 6. The semiconductor
substrate 1 is exposed along an edge 12 of the semiconductor chip 1a,
because boundaries of a plurality of chips formed on a wafer are defined
by scribed lines for dieing the chips out of the wafer.
When the inner lead 11 is bonded to the semiconductor chip 1a at bump 9 on
pad 13, heat of the bonding tool 14 is conducted to the inner lead 11,
thereby causing the inner lead 11 to sag down due to thermal expansion
thereof. Further, the eutectic alloy formed between the bump 9 and inner
lead 11 and tin of the tin-plated inner lead 11 are melted by the heat of
the bonding tool 14 and sag on the semiconductor chip to pressure it or
cause the positional offset of the bonding tool 14. This deteriorates the
aforesaid problem. In the worst case, a crack occurs in an insulation film
10 formed on the metal interconnection 17, resulting in a short circuit
between the metal interconnection 17 and the inner lead 11 or between the
inner lead 11 and the edge 12 of the semiconductor chip 1 or in the
corrosion of the metal interconnection 17 due to moisture penetrating from
the crack.
There has been proposed a method for forming a metal interconnection in an
indentation such as formed between dummy electrodes to prevent the metal
interconnection from being slidingly offset when a lateral stress is
applied to the semiconductor chip. However, no consideration is given to
the aforesaid problem concerning the bonding of the inner lead. The dummy
electrodes are useless to prevent the inner lead from sagging due to heat
or from being short-circuited to the edge of the semiconductor chip.
Further, there is a possibility that a plurality of inner leads are
short-circuited to one dummy electrode since the inner leads cross the
dummy electrode extending parallel to the metal interconnection. In such
an event, an unintended signal is applied to the pad via the dummy
electrode, resulting in an erroneous operation of the semiconductor
device.
SUMMARY OF THE INVENTION
The present invention provides a semiconductor device comprising: a
semiconductor chip having a semiconductor substrate, an insulation film, a
field oxide film and pads formed on a surface thereof; bumps respectively
formed on the pads; inner leads bonded to the semiconductor chip with
intervention of bumps; a metal interconnection formed in an indentation
which is formed between the pads and an edge of the semiconductor chip by
removing part of the insulation film and/or the field oxide film of the
semiconductor chip; and a pair of dummy electrodes respectively formed
between each of the pads and the metal interconnection and between the
metal interconnection and the edge of the chip at a higher elevation than
the metal interconnection and spaced apart a predetermined distance from
the metal interconnection, the pair of dummy electrodes being provided for
each of the inner leads, which is located thereabove.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic plan view illustrating connection between a
semiconductor chip and inner leads in accordance with the present
invention;
FIG. 2 is a schematic sectional view taken along a line A-A' in FIG. 1 (in
case that the semiconductor chip is of a double-layer dummy electrode
structure);
FIG. 3A is a schematic sectional view taken along a line A-A' in FIG. 1 (in
case that the semiconductor chip is of a single-layer dummy electrode
structure);
FIG. 3B is a schematic sectional view taken along a line A-A' in FIG. 1 (in
case that the semiconductor chip is of a double-layer dummy electrode
structure);
FIG. 4 is a schematic sectional view taken along a line A-A' in FIG. 1 (in
case that the semiconductor chip is of another double-layer dummy
electrode structure);
FIG. 5 is a diagram for explaining an inner lead bonding process;
FIG. 6 is a schematic plan view illustrating connection between a
semiconductor chip and an inner lead in a prior art; and
FIG. 7 is a schematic sectional view taken along a line B-B' in FIG. 6.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
A semiconductor chip according to the present invention includes various
devices such as a transistor, a capacitor and a resistor and circuits,
which are interconnected via interconnection layers and protected by an
insulation film or the like. Bumps are preferably formed on pads which are
exposed oh a surface of the semiconductor chip formed with these devices
and circuits. Materials to be used for the formation of the pads are not
particularly limited, but examples thereof include conductive materials
such as Al, TiW, Au, Ti and Cu which are typically used as an electrode
material. Exemplary materials for the bumps include solder, gold, and the
aforesaid materials for the pads. Inner leads are bonded to the pads of
the semiconductor chip via the bumps for fabrication of the semiconductor
device.
In the semiconductor device of the present invention, a metal
interconnection such as a power supply line is disposed between the pads
formed on the semiconductor chip and a chip edge. The metal
interconnection is provided: (1) in an indentation formed as reaching a
surface of the semiconductor substrate by removing part of an insulation
film of the semiconductor chip in a region where no field oxide film is
provided; (2) in an indentation formed as reaching a surface of the field
oxide film by removing part of the insulation film in a region where the
field oxide film is formed or in an indentation formed as reaching the
surface of the semiconductor substrate by removing parts of the insulation
film and the field oxide film; or (3) in an indentation formed directly on
the semiconductor substrate by etching part of a surface portion of the
semiconductor substrate. Materials to be used for the metal
interconnection are not particularly limited, but examples thereof include
Al, AlSi, AlCu, AlSi/TiW, AlTi, TiN and the like which are typically used
as a conductive material. The thickness and width of the metal
interconnection vary depending on the size and the like of a semiconductor
device to be obtained. For example, the thickness is preferably about 500
nm to about 1,200 nm, more preferably about 700 nm to about 900 nm. The
width is preferably about 0.2 .mu.m to about 20 .mu.m.
A pair of dummy electrodes are respectively formed between each of the pads
and the metal interconnection and between the metal interconnection and
the edge of the semiconductor chip in the state of single-layer or
double-layer, or multiple-layer structure. Pairs of dummy electrodes
corresponding to the respective inner leads are preferably separated from
each other as shown in FIG. 1. The configuration of the dummy electrodes
is not particularly limited as long as the dummy electrodes are spaced
apart a predetermined distance from the metal interconnection around the
intersections of the inner leads and the dummy electrodes. Each of the
dummy electrodes is preferably formed into a rectangular shape which
extends generally parallel to the metal interconnection. Exemplary
materials for the dummy electrodes include Al, AlSi, AlCu, AlSi/TiW, AlTi,
TiN, polysilicon, silicides of polysilicon and high-melting-point metals,
and polycides of such. silicides and polysilicon. The thickness and width
of the dummy electrodes are about 200 nm to about 1,000 nm and about 0.2
.mu.m to about 10 .mu.m, respectively.
Where the dummy electrodes are of the single-layer structure, the dummy
electrodes are formed oh the field oxide film so that the upper faces
thereof are located at a higher elevation than the metal interconnection,
or the dummy electrodes are formed on a region where there is no field
oxide film so that the upper faces thereof are located at a higher
elevation than the metal interconnection. The dummy electrodes may be
formed, for example, along with a gate electrode of a transistor to be
formed on the semiconductor substrate in a single process by using the
same material as the gate electrode. The configuration of the dummy
electrodes is such that the gate electrode can be electrically isolated
therefrom. Alternatively, the dummy electrodes can be formed along with an
interconnection layer other than the gate electrode, the pads or the like
in a single process by using the same material. Instead of dummy
electrode, the insulaters like SiO.sub.2, SiN, etc., can form the
elevation difference between the upper surface of the insulaters and the
surface of the metal by adding the extra process steps.
Where the dummy electrodes are of the double-layer structure, first layers
of the respective dummy electrodes may be formed in the aforesaid manner,
on which second layers thereof are formed with intervention of an
insulation film. In this case, the upper faces of the second layers of the
dummy electrodes may be located at a higher elevation than the metal
interconnection. An interlayer insulation film for covering the devices
formed on the semiconductor substrate can be used as the insulation film
and may be, for example, formed of a single-layer film or lamination of
SiO.sub.2, SiN, BPSG, BSG and the like. Where the dummy electrodes are to
be formed on the interlayer insulation film, the dummy electrodes may be
formed, for example, along with the metal interconnection for
interconnecting the devices in a single process by using the same material
as the metal interconnection. The configuration of the dummy electrodes is
such that the metal interconnection can be electrically isolated
therefrom.
Even if the inner leads sink or sag, the inner leads are supported by the
dummy electrodes which are electrically isolated from the metal
interconnection and, therefore, direct contact to the edge of the
semiconductor or the metal interconnection can be prevented because the
dummy electrodes are located at a higher elevation than the metal
interconnection. Further, short circuit between an inner lead and a dummy
electrode only causes the dummy electrode to be kept at the same potential
as the inner lead and may not produce any adverse effect, because the
respective pairs of dummy electrodes are separated from each other. The
provision of the second-layer dummy electrode on the first-layer dummy
electrode increases the elevation difference between the upper surface of
the second-layer the dummy electrode and the surface of the metal
interconnection, thereby more assuredly preventing the metal
interconnection from contacting the inner lead or the edge of the
semiconductor chip. The amount of the sag of the inner leads should be
estimated in consideration of the bonding temperature and the coefficient
of linear thermal expansion of the inner lead material to determine an
appropriate depth of the indentation. The depth of the indentation should
be greater than the estimated amount of the sag. The construction of the
dummy electrodes (i.e., whether the dummy electrodes are of the
single-layer structure or of the double-layer structure and whether or not
the field oxide film is provided under the metal interconnection) may be
appropriately determined depending on the depth of the indentation.
Where the metal interconnection which is formed directly on the
semiconductor substrate is applied with a potential different from that to
be applied to the semiconductor substrate, an impurity diffusion layer
having a conductivity type different from that of the semiconductor
substrate is preferably formed under the metal interconnection to isolate
the metal interconnection from the semiconductor substrate. Where the
metal interconnection is to be applied with the same potential as that to
be applied to the semiconductor substrate, an impurity diffusion layer
having the same conductivity type as that of the semiconductor substrate
may be formed under the metal interconnection. The diffusion layer may be
formed, for example, along with a diffusion layer of a transistor to be
formed on the semiconductor substrate. In this case, the concentration of
a P-type or N-type impurity is preferably about 10.sup.15 ions/cm.sup.3 to
about 10.sup.20 ions/cm.sup.3.
Although the aforesaid explanation for the semiconductor device in
accordance with the present invention is directed to the tape carrier
package (TCP), the present invention can be applied to a wire-bonded
semiconductor device in substantially the same manner.
With reference to the attached drawings, the present invention will be
described by way of embodiments thereof. It should be understood that the
embodiments are not limitative of the present invention.
EXAMPLE 1
As shown in FIGS. 1 and 2, the semiconductor device of the present
invention essentially consists of a silicon substrate 1, an about 1.0
.mu.m-thick field oxide film 2 formed on the silicon substrate 1, a
diffusion layer 3 formed in the silicon substrate 1, about 0.5 .mu.m-thick
first dummy electrodes 4 formed on the field oxide film 2, and about 0.9
.mu.m-thick insulation films 5 formed on the first dummy electrodes 4.
Second dummy electrodes 8 are provided on the respective first dummy
electrodes 4 with intervention of the insulation films 5. An indentation 6
is formed directly on the diffusion layer 3 of the silicon substrate 1
between the first dummy electrodes 4 (second dummy electrodes 8), and a
metal interconnection 7 is formed in the indentation 6. A bump 9 is
provided on a pad 13 formed on the silicon substrate 1, and an inner lead
11 extending across the second dummy electrodes 8 and the metal
interconnection 7 is bonded to the bump 9. Where the metal interconnection
7 is to be applied with the same potential as that to be applied to the
silicon substrate 1, the diffusion layer 3 is preferably of the same
conductivity type as the silicon substrate 1. Where the metal
interconnection 7 is to be applied with a potential different from that to
be applied to the silicon substrate 1, the diffusion layer 3 is preferably
of a conductivity type different from that of the silicon substrate 1.
Since the metal interconnection 7 is formed directly on the silicon
substrate 1 in the semiconductor device of the above, the elevation
difference between the second dummy electrodes 8 on the field oxide film 2
and the metal interconnection 7 equals the sum (1.9 .mu.m) of half the
thickness of the field oxide film 2 (0.5 .mu.m), the thickness (0.5 .mu.m)
of the first dummy electrode 4 and the thickness (0.9 .mu.m) of the
insulation film 5. Therefore, the elevation difference is significantly
greater than the thickness of the metal interconnection 7. Even if the
inner lead 11 sags to break the insulation film 10, the second dummy
electrodes 8 on the field oxide film 2 support the inner lead 11, thereby
preventing the inner lead 11 from being short-circuited to the metal
interconnection 7 or a chip edge 12.
There will next be explained a fabrication method for the semiconductor
device as shown in FIG. 2.
An about 1.0 .mu.m-thick field oxide film 2 is formed on a silicon
substrate 1 by an LOCOS method. At this time, the field oxide film 2 is
not formed in a region where a metal interconnection 7 is to be formed.
In turn, a polysilicon layer is deposited in a thickness of about 0.5 .mu.m
on the entire surface of the resulting substrate with intervention of a
gate insulation film, and patterned into a desired configuration to form a
gate electrode (not shown) and first dummy electrodes 4 which are to be
located on the both sides of the metal interconnection 7 to be formed in a
later process.
To form a source/drain diffusion layer (not shown), ion implantation is
performed. At this time, a diffusion layer 3 is also formed in a region
where no field oxide film 2 is formed. An interlayer insulation film 5 is
formed on the gate electrode and the first dummy electrodes 4.
Simultaneously with the formation of a contact hole in the interlayer
insulation film 5, an indentation 6 is formed as reaching the silicon
substrate 1 formed with the diffusion layer 30 between the first dummy
electrodes 4.
Subsequently, a conductive layer is formed on the resulting substrate
including the contact hole and the indentation 6, and patterned into a
desired configuration to form a pad 13, second dummy electrodes 8 and the
metal interconnection 7. An insulation film 10 is formed on the resulting
substrate including the pad 13, the metal interconnection 7 and the second
dummy electrodes 8 to protect the surface of the semiconductor chip.
Thereafter, a bump 9 for connecting to the pad 13 of the semiconductor chip
is formed by a known method. The inner lead 11 is bonded to the bump 9 by
using a bonding tool or the like. Thus, the semiconductor device is
completed.
EXAMPLE 2
There will next be described another semiconductor device in accordance
with the present invention. As shown in FIG. 3A, the semiconductor device
essentially consists of a silicon substrate 1, an about 1.0 .mu.m-thick
field oxide film 2 formed on the silicon substrate 1 and an about 0.9
.mu.m-thick insulation film 5 formed on the field oxide film 2. An
indentation 6 is formed by removing part of the insulation film 5. A metal
interconnection 7 is formed in the indentation 6, and about 0.5
.mu.m-thick dummy electrodes 8 are disposed parallel to the metal
interconnection 7 on the insulation film 5. Another insulation film 10 is
provided on the dummy electrodes 8. A bump 9 is disposed on a pad 13
formed on the silicon substrate 1, and an inner lead 11 extending across
the dummy electrodes 8 and the metal interconnection 7 is bonded to the
bump 9.
In the semiconductor device of the above, the metal interconnection 7 is
formed on the field oxide film 2 as described above. Therefore, the
elevation difference between the dummy electrodes 8 and the metal
interconnection 7 equals the thickness (0.9 .mu.m) of the insulation film
5, which is greater than the thickness of the metal interconnection 7.
Even if the inner lead 11 sags to break the insulation film 10 when the
inner lead 11 is bonded to the bump 9, the dummy electrodes 8 formed on
the insulation film 5 support the inner lead 11, thereby preventing the
inner lead 11 from being short-circuited to the metal interconnection 7 or
a chip edge 12.
The semiconductor device may be fabricated in substantially the same manner
as the aforesaid fabrication method.
EXAMPLE 3
There will next be described still another semiconductor device in
accordance with the present invention.
As shown in FIGS. 1 and 4, the semiconductor device of the present
invention essentially consists of a silicon substrate 1, an about 1.0
.mu.m-thick field oxide film 2 formed on the silicon substrate 1, a
diffusion layer 3 formed in the silicon substrate 1, about 0.5 .mu.m-thick
first dummy electrodes 4 formed on the field oxide film 2, and about 0.9
.mu.m-thick insulation films 5 formed on the first dummy electrodes 4.
Second dummy electrodes 8 are provided on the respective first dummy
electrodes 4 with intervention of the insulation films 5. An indentation 6
is formed on a region in which the field oxide film 2 is not formed on the
silicon substrate 1 between the first dummy electrodes 4 (second dummy
electrodes 8), and a metal interconnection 7 is formed in the indentation
6. A bump 9 is provided on a pad 13 formed on the silicon substrate 1, and
an inner lead 11 extending across the second dummy electrodes 8 and the
metal interconnection 7 is bonded to the bump 9.
Since the metal interconnection 7 is formed on a region in which a field
oxide film 5 is not formed on the silicon substrate 1 in the semiconductor
device of the present invention, the elevation difference between the
second dummy electrodes 8 on the field oxide film 2 and the metal
interconnection 7 equals the sum (1.0 .mu.m) of half the thickness of the
field oxide film 2 (0.5 .mu.m), and the thickness (0.5 .mu.m) of the first
dummy electrode 4. Therefore, the elevation difference is significantly
greater than the thickness of the metal interconnection 7. Even if the
inner lead 11 sags to break the insulation film 10, the second dummy
electrodes 8 on the field oxide film 2 support the inner lead 11, thereby
preventing the inner lead 11 from being short-circuited to the metal
interconnection 7 or a chip edge 12.
There will next be explained a fabrication method for the semiconductor
device as shown in FIG. 4. An about 1.0 .mu.m-thick field oxide film 2 is
formed on a silicon substrate 1 by an LOCOS method. At this time, the
field oxide film 2 is not formed in a region where a metal interconnection
7 is to be formed.
In turn, a polysilicon layer is deposited in a thickness of about 0.5 .mu.m
on the entire surface of the resulting substrate with intervention of a
gate insulation film, and patterned into a desired configuration to form a
gate electrode (not shown) and first dummy electrodes 4 which are to be
located on the both sides of the metal interconnection 7 to be formed in a
layer process.
To form a source/drain diffusion layer (not shown), ion implantation is
performed. At this time, a diffusion layer 3 is also formed in a region
where no field oxide film 2 is formed. If formation of the diffusion layer
3 is to be avoided, an additional mask may be formed to prevent impurity
ions from being implanted into the region. An interlayer insulation film 5
is formed on the gate electrode and the first dummy electrodes 4. In the
interlayer insulation film 5, a contact hole (not shown) is formed.
Subsequently, a conductive layer is formed on the resulting substrate
including the contact hole and the indentation 6, and patterned into a
desired configuration to form a pad 13, second dummy electrodes 8 and the
metal interconnection 7. An insulation film 10 is formed on the resulting
substrate including the pad 13, the metal interconnection 7 and the second
dummy electrodes 8 to protect the surface of the semiconductor chip.
Thereafter, a bump 9 for connecting to the pad 13 of the semiconductor chip
is formed by a known method. The inner lead 11 is bonded to the bump 9 by
using a bonding tool or the like. Thus, the semiconductor device is
completed.
EXAMPLE 4
As shown in FIG. 3B, the semiconductor device is constructed in such a
manner that the dummy electrode of the device shown in FIG. 3A are formed
in a double-layer structure shown in FIG. 4.
In accordance with the present invention, even if the inner lead sinks or
sags, the dummy electrodes support the inner lead to prevent the inner
lead from being short-circuited to the metal interconnection and/or the
edge of the semiconductor chip because the dummy electrodes are disposed
at a higher elevation than the metal interconnection. Further, the dummy
electrodes of the single-layer or double-layer structure can be formed
simultaneously with the formation of other interconnection. Therefore, an
additional process step is not required.
Even if breakage of a protection film formed on a dummy electrode causes
the inner lead to be short-circuited to the dummy electrode, the dummy
electrode is only kept at the same potential as that applied to the pad,
because the dummy electrode is electrically isolated from the other
portions. Therefore, no erroneous operation occurs in the semiconductor
device.
Where the metal interconnection is provided directly on the semiconductor
substrate in the indentation, the short circuit between the metal
interconnection and the inner lead located above the metal interconnection
can be more assuredly prevented. In addition, the formation of the metal
interconnection in the indentation can be readily achieved by modifying
the configuration of a photomask for the formation of the field oxide
film.
Since there is no fear that the inner lead contacts or is short-circuited
to the semiconductor chip during the inner lead bonding process, the
setting of the bonding conditions can be facilitated, and the yield and
reliability in the inner lead bonding process can be improved.
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